The presence of mold and mildew in residential and commercial buildings is an issue of increasing concern. Aside from being unsightly, mold has allegedly been linked to a myriad of health conditions, including allergic reactions, infections, irritation of the mucous membranes and respiratory system, detrimental effects on the central nervous system (e.g., disorientation, dizziness, and diminished reflexes and attention span), and desensitivity or hypersensitivity to mold over time. So-called “toxic” molds, while less prevalent, are alleged to contribute to more serious conditions, including immune system suppression, organ damage, blood vessel rupture, depression, infertility, and cancer.
Mold spores are ubiquitous in both indoor and outdoor air. Virtually any surface, inorganic as well as organic, having residual moisture or dampness can provide the necessary environment for these mold spores to survive and potentially grow. With sufficient moisture, accumulated dust or even the surface itself, upon which mold spores happen to land, can serve as a food source for mold growth.
For the above reasons, the construction industry is continually challenged with the prevention of mold growth, mainly through the minimization or elimination of sources of moisture. These sources can stem from wet building materials, leakage through the building envelope or in the plumbing system, HVAC condensation, or flooding. Many of the problems leading to mold growth occur during the construction phase, when materials are installed without sufficient regard for minimizing the exposure to moisture.
Gypsum is among the most important and prevalent materials used in the housing and building construction industry. The conventional manufacturing of gypsum board for use in wall and roofing materials is well known and generally involves forming a core layer of wet plaster slurry between two sheets of a heavy paper (e.g., multi-ply paper) or cardboard material. When the wet plaster core sets and is dried, a strong, rigid, and fire-resistant building material results. The paper- or cardboard-based sheets that sandwich the gypsum core are referred to in the industry as facing paper. Unfortunately, conventional gypsum facing paper is often not sufficiently water resistant to prevent the growth of mold and mildew when the board is subjected to severe moisture stresses.
The modification of facing materials on a number of substrates and for a variety of purposes is known in the art. For example, U.S. Pat. No. 2,806,811 describes the addition of small quantities of resinous materials to the plies that make up the facing paper of gypsum board, in order to prevent delamination and splitting of the plies.
U.S. Pat. No. 3,616,144 describes a tile comprising a resin-bonded core portion and a facing layer. The facing layer is a fibrous material that may be impregnated with a resin to provide strength.
U.S. Pat. No. 4,470,877 describes a calcium sulfate-filled paper for use in making gypsum wallboard with reduced energy requirements.
U.S. Pat. No. 4,764,420 describes a barrier latex polymer-coated facing sheet of fibrous material to preserve the insulating properties of a rigid plastic foam core.
U.S. Pat. No. 5,079,078 describes a laminated panel having a gypsum or cement core and outwardly disposed, fire-resistant “skins” comprising a high density composite of glass fibers and resin.
U.S. Pat. No. 5,397,631 describes a fibrous mat-faced gypsum board that is coated with a substantially humidity- and water-resistant resinous coating containing a latex polymer.
U.S. Pat. No. 5,791,109 and related patents describe a gypsum board comprising a core that is faced with a fibrous mat that is made of woven or non-woven glass or synthetic fibers, in order to improve water and fire resistance.
U.S. Pat. No. 6,187,697 describes nonwoven resin-bound fibrous mats that can be used to face a myriad of surfaces to provide reinforcement and dimensional stability.
U.S. Pat. No. 6,689,451 describes a substrate that is laminated with cellulose paper that may be penetrated with resin. To prevent delamination caused by differential stresses, a polymeric film (e.g., polyurethane, acrylic, polyester, and others) is incorporated between the substrate and the paper.
U.S. Pat. No. 6,770,354 describes a moisture tolerant structural panel comprising a fibrous mat-faced gypsum board wherein the outer surface of the mat has a coating that is a mixture of a mineral pigment, an inorganic binder and a latex polymer binder.
U.S. Published Application No. 2003/0236041A1 describes a laminated sheet to improve fire resistance in various interior applications. The laminated sheet comprises a resin-impregnated paper that is stacked onto one or both faces of a sheet base that is obtained by impregnating a fire retardant material (e.g., glass cloth) with a resin, optionally containing tetrabromobisphenol A.
In view of the above disclosures, there is an ongoing need in the art for gypsum board construction materials having improved mold- and/or moisture resistance, as well as a potential for improved fire resistance. Ideally, such gypsum materials should be made in a cost-efficient manner with little or no alteration of existing processing conditions and production facilities.